2.8a Questions

Now that you have invested some time in the Dutchess Country metamorphosed shales, you are in a position to consider and answer the following questions. Use the equilibrium assemblages in the Spear-Cheney KFMASH petrogenetic grid to help answer the questions.

(1) Samples DC-05 (Bt-Chl-Grt) and DC-10 (Chl-Cld-Grt) were both collected in the Grt Zone near one another, yet they have different mineral assemblages. What is a possible explanation for this difference?

Pick one and press "Enter".
(a) One of the rocks is a glacial erratic and comes from a different metamorphic zone.
(b) One or both of the samples does not represent of chemical equilibrium.
(c) Retrograde metamorphism has changed one or both of the samples during during cooling and exhumation.
(d) The two rocks are both at equilibrium, but have different bulk compositions.
(e) Samples were mixed up and the two samples do not come from near one another.